package com.hackerrank.contests.nov13.challenges.bdaygift;

import java.util.Scanner;

public class Solution {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int N = in.nextInt();
		long S = 0;
		for(int i = 0; i < N; i++)
			S += in.nextInt();
		System.out.printf("%.1f", S / 2.0);
	}
}
